1. Field of the Invention
The present invention pertains to a solid oxide fuel cell device, and more particularly to a solid oxide fuel cell device in which electrical power is produced by reacting fuel and oxidant gas for electrical generation.
2. Description of the Related Art
A fuel cell apparatus and operating method for same is described in Patent Application JP 2004-319420A (Patent Document 1). The fuel cell apparatus set forth here is constituted to pass through multiple steps for reforming fuel in a reformer, being: a partial oxidation reforming reaction step (the POX step), an auto thermal reforming reaction step (the ATR step), and a steam reforming reaction step (the SR step), then transition to electrical power generation.
In the fuel cell apparatus set forth in Patent Document 1, a reformer is disposed within a fuel cell module; this reformer is heated by combusting, at the top end portion of each fuel cell, the fuel gas (off-gas) which has remained unused for electrical generation in each of the fuel cells. Note that in the present application, the type of fuel cell device in which off-gas combustion heat is used to heat the reformer to a temperature at which reforming is possible is referred to as an “off-gas fuel cell burner type” of fuel cell device.
In such off-gas fuel cell burner-type fuel cell device, heating of a reformer at room temperature is done at startup by combusting off-gas (because electrical generation is not done at startup, this corresponds to all the supplied fuel). When the catalyst temperature inside the reformer is raised to approximately 300° C. by this heating, a partial oxidation reforming reaction (the POX step) occurs in the reformer, in which fuel and reforming air are reacted. Because the partial oxidation reforming reaction is an exothermic reaction, when a partial oxidation reforming reaction occurs inside the reformer, the reformer is strongly heated by this reaction heat and off-gas combustion heat.
When the reformer temperature further rises due to this heating, reforming steam is supplied into the reformer, and in the reformer a steam reforming reaction occurs in which fuel and steam react. This steam reforming reaction is one in which hydrogen can be more efficiently produced than in the partial oxidation reforming reaction, but it does not occur unless the temperature of the catalyst in the reformer rises to approximately 600° C. Also, because the steam reforming reaction is an endothermic reaction, the catalyst temperature drops rapidly if the temperature of the reformer and inside the fuel cell module has not risen sufficiently, and stable steam reforming cannot be performed. In a fuel cell device of the off-gas combustion burner type, air and steam for reforming is supplied to the reformer after the POX step has been performed, and the partial oxidation reforming reaction and steam reforming reaction are caused to occur simultaneously within the reformer (the ATR step). In this ATR step, the temperatures inside the reformer and the fuel cell module are raised while maintaining an appropriate balance between the exothermic heat from the partial oxidation reforming reaction, the endothermic heat from the steam reforming reaction, and the off-gas combustion heat.
When the temperature inside the reformer and the fuel cell module rise sufficiently due to the ATR step, supply of reforming air is stopped, and in the reformer only the steam reforming reaction takes place (the SR step). Thereafter, when the temperature of each fuel cell is raised by the SR step to a temperature at which electrical generation is possible, the fuel cell device transitions to the electrical generation step, wherein hydrogen is only produced by the steam reforming reaction.
Thus in oxidant gas combustion cell burner types of fuel cell device not provided with a dedicated means for heating the reformer, the reformer is rapidly heated from room temperature by the POX step, which utilizes a partial oxidation reforming reaction occurring at a comparatively low temperature, following which reforming (the ATR and SR steps) using the steam reforming reaction is executed.